The present invention relates to a storage system including a plurality of storage devices with the interrelationship established thereamong for data recovery, and a data reading method and a data reading program regarding the same.
A storage system recently developed is a type operating a plurality of magnetic disk devices in parallel, so that a data reading/writing process requested by a host is increased in speed, and the reliability is improved with the redundant structure. Such a storage system is generally referred to as RAID (Redundant Arrays of Inexpensive Disks). The RAID structure varies in level, i.e., level 1 to level 5, details of which are described in Non-patent Document 1 below.
In Non-patent Document 2, described is another type of RAID structure derived by expanding the RAID structure of level 4 of Non-patent Document 1. The RAID structure is the one offering a guarantee of data storage even if any two disk devices fail. Specifically, for guaranteeing as such, used are two types of parity data: one is parity data as a calculation result of exclusive OR of data stored in the respective storage devices forming a logical unit; and the other is parity data as a calculation result of exclusive OR of data and a multiplied value of the other parity data and a specific coefficient.
In the storage system, other than a Fibre Channel disk device, an ATA (AT attachment) disk device is getting popular. The problem is that an ATA disk device is lower in cost than a Fibre Channel disk device, but also lower in reliability and thus fails easily. Thus, it is highly possible that any two disk devices fail at the same time, i.e., double failure occurs. Moreover, the capacity per disk device has been steadily increasing, resulting in longer time taken for data recovery in any failed disk device utilizing the RAID technology. Thus, even if any high-reliable disk devices are in use, the possibility of double failure remains high. In consideration thereof, as the technology of Non-patent Document 2, measures to be taken against multiple failures will become increasingly important from now on.
In Patent Document 1, described is a storage system offering a guarantee of response time with respect to a data request coming from a host even if any failure occurs to disk devices. With this storage system, no matter if any failure is occurring to disk devices, any other data needed for recovering the requested data is always read in parallel. Even if reading of the requested data does not work, the requested data is favorably recovered without newly reading redundant data from the disk devices.
Herein, Non-patent Document 1 is “a Case for Redundant Arrays of Inexpensive Disks (RAID)” authored by D. Patterson, proceedings of the 1988 ACM SIGMOD international conference ON Management of data, PP. 109 to 116, 1988.
Non-patent Document 2 is “EVENODD: an Optimal Scheme for Tolerating Double DISK Failures in RAID Architectures” authored by M. Blaum, Proceedings of the 21st Annual International Symposium ON Computer Architecture, PP. 245 to 254, 1994.
Further, Patent Document 1 is JP-A-10-247133.